The manufacturing processes involving the formation of lubricating oil additives frequently involve the reaction of at least two reagents in an oil diluent-solvent which results in an oil solution of the additive. This solution frequently is hazy due to the presence of difficulty removable reaction products, impurities and/or unreacted reagents which haze must be reduced to market acceptable levels prior to sale or incorporation into the lubricating oil.
Representatives of such additives are sulfonate salts, calcium phenate and salts of dihydrocarbyldithiophosphic acids which are useful in automotive oils, industrial oils, hypoid gear oils, and automatic transmission fluids, to impart dispersancy, oxidation resistance, extreme pressure properties, corrosion resistance, and detergency to the oil.
The manufacture of satisfactorily clear, odorless, and stable salts of dihydrocarbyldithiophosphoric acids and in particular the zinc salt has been found to be particularly difficult in the past and sensitive to a variety of processing conditions. While many process improvements have been made, the products of current processes tend to be hazy. The haze does not appear to harm engines or processing equipment. Since the haze in the product can be masked by blending, the hazy zinc product can be blended into finished oils or multiadditive packages. However, the hazy zinc dehydrocarbyl dithiophosphate product cannot be sold in a concentrate or single additive package and when blended into mixed additive packages contributes to reduced shelf life of the package.
U.S. Pat. No. 3,562,306 teaches the use of zinc nitrate, zinc chloride, zinc sulfate and the like to promote the reaction between zinc oxide and the dihydrocarbyl dithiophosphoric acid. U.S. Pat. No. 3,290,347 teaches the use of water soluble fatty acids and water soluble metal salts of fatty acids to accelerate the reaction between the metal compound and the dithiophosphoric but both of these approaches have been reported to suffer the disadvantage that the colloidal zinc compound particle haze will form in the presence of these accelerants.
According to U.S. Pat. No. 4,215,067 this disadvantage of haze formation is reduced if not overcome by addition of a surface active agent to the reaction mixture at or before the neutraliation of the dihydrocarbyl dithiophosphoric acid with the zinc compound to prevent or minimize have formation. Typically, the current techniques for current production still use the procedures of U.S. Pat. No. 4,377,527 which filters or centrifuges the zinc product to remove the residual solids (col. 4, lines 29-30).
Polyacrylamide (PAM)-treated perlite has been used in the filtration of zinc dialkyl dithiophosphate (ZDDP) and other lube oil additives with the offsetting results that although the purity of ZDDP increased, the filtration rate when down ("EFFECT OF SURFACTANTS ON THE PROPERTIES OF PERLITIC POWDER DURING THE FILTRATION OF ADDITIVES TO OILS" by L. I. Rudenko, V. Yu. Tretinnik, N. N. Kruglitskii, and G. I. Sergeev (All-Union Sci.-Res. Design-Constr. Inst. of Petr. Refining & Petrochem. Ind., Keiv, USSR) Khim. Tekhnol. (Kiev) #1:16-18 (1978)).
PAM has also been used: to break oil-clay-water emulsions ("ACTION OF POLYACRYLAMIDE ON THE STABILITY OF A CLAY SUSPENSION IN TRANSFORMER OIL" by N. N. Kruglitskii and I. N. Poraiko Ukr. Khim. Zh. 40#6:654-655 (1975)); to aggregate iron in substantially water-free used lubricating oil (Jap. Published Patent Application No. 53-34806 of 1978); and, to dewater a petroleum oil-water-solids sludge prior to filtration (U.S. Pat. No. 4,417,976 col. 2, line 13 to col. 3, line 33).
Unfortunately, none of these references suggest a means to improve the mechanical removal of unconsumed reagents and reaction byproduct solids from an oil solution of a salt of an organic moiety to provide a haze free lubricating oil additive solution.
Accordingly, it appears a need still remains for producing substantially haze-free lubricating oil additives such as oil solutions of zinc dihydrocarbyl dithiophosphate.